i'd be more concerned that the footings wouldnt be up to snuff. you'll need to insulate under the floor, too. is it close to ground level or can you work from underneath?

Thank you, Deborah! Actually our current foundation is a concrete slab with foundation wall. I've been wondering the same thing: if we should change the structure to a crawl space. Do you mind me asking how much the cost is for this part of your project?

nnigrt, I don't have access from below. It's a concrete slab with foundation wall. I'm thinking the footings should be OK since they pulled a permit at the time. The concrete is ground level, but the rest of the house is about 5" higher. A contractor suggested doing a subfloor-ish framing on top of the concrete with 2x4s, insulate these with foam spray, and then install flooring on top.

You can do what the contractor says to frame over the existing concrete and it does work - just to let you know in case you go that route that it is a normal type process that is done all the time. The issue becomes HVAC and how you plan to run the ductwork to heat and cool the space.

Circumstances differ for every project and property so I am not sure the cost here would be relevant. We are working on a property that is 5 acres, the house is literally in the middle of the woods with no good access to the back side to get equipment and materials in, it is on a slope and we had to jack hammer out boulders to get a foundation in. We don't price by portions of a project, but I would say with a 4' foundation, the grading work, brick and materials, termite treatment and all water proofing the cost is in the $10k range.

Thank you so much, Deborah! That's very helpful! The reason I'm thinking about turning it into a crawl space is because of the HVAC. Without access from below, it's very difficult to route ductwork to that room. We might be able to route it through the ceiling, but I just wanted to know how much the other option (adding crawl space) would cost. Thank you again!

You are welcome. Good luck with your project. I know it adds cost, but we have tried to use mini-split systems in sunrooms and they are so ugly (sorry to offend anyone that has these) and they are just not efficient.